Technical Field
An aspect of the present invention relates to a glass substrate for mask blanks for use in various kinds of lithography, and to its production method. An aspect of the present invention is favorable for a glass substrate for mask blanks to be used in lithography using EUV (extreme ultraviolet) light (hereinafter abbreviated as “EUVL”) (hereinafter this is abbreviated as “glass substrate for EUVL mask blank”).
An aspect of the present invention is also favorable for a glass substrate for mask blanks for use in lithography using an already-existing transmission optical system, for example, for a glass substrate for mask blanks for lithography using an ArF excimer laser or a KrF excimer laser.
Background Art
With the recent tendency toward high-density and high-precision ultra-LSI devices, the specifications required for the main surface of the glass substrate for mask blanks for use in various kinds of lithography are becoming severer year by year. In particular, with the wavelength of the light from the exposing source being shorter, the requirements for the profile accuracy (surface roughness) of the main surface and for the absence of the defects (particles, scratches, pits, etc.) in the surface are becoming severer, and a glass substrate having an extremely small surface roughness and having few microdefects is desired
For example, in a case of a glass substrate for mask blanks for use in lithography using an ArF excimer laser as the light from an exposing source, the root-mean-square surface roughness (RMS) of the main surface may be required to be 0.15 nm or less and the number of the defects therein having a polyethylene latex particle diameter-equivalent size of 50 nm or more may be required to be 5 or less.
Accordingly, the main surface of a glass substrate for mask blanks is chemomechanically polished so as to have a desired surface roughness, by using a particulate polishing agent such as colloidal silica, cerium oxide, zirconia or alumina.
In the case where a subject to be polished, such as the main surface of a glass substrate for mask blanks or the like, is polished, using a polishing agent, the particulate polishing agent would adhere to the surface of the polished subject to remain on the polished subject. Consequently, for the purpose of removing the polishing agent remaining on the polished subject, in general, the polished subject is washed in wet.